Problem: Which of these numbers is composite? ${2,\ 7,\ 17,\ 33,\ 67}$
Solution: A composite number is a number that has more than two factors (including 1 and itself). 2, 7, 17, and 67 each have only two factors. The factors of 33 are 1, 3, 11, and 33. Thus, 33 is the composite number.